The present invention relates to a cathode ray tube and a process for producing the same, and more particularly to a process of forming an antistatic and non-glare coating on the outer surface of the panel of a cathode ray tube.
Glasses or plastics are widely used for display devices, such as cathode ray tubes and liquid crystal display devices. Due to the insulation property of these materials, an electrostatic charge is accumulated on the outer surface of the front panel during or after the operation of the devices. Thus, dust is attracted and accumulated on the outer surface, which deteriorates the luminance and contrast of the cathode ray tube. Also, if the outer surface of the cathode ray tube is touched, operators may be shocked by an electrostatic charge present on the panel's surface.
In addition, the front panel's outer surface is glossy and liable to strongly reflect external light, making it difficult to view images formed thereon.
Thus, various methods have been proposed to prevent these display panels from being electrically charged and reflecting external light.
In order to prevent the surfaces of the display panels from being charged, there are methods of forming a transparent electroconductive coating on the panel's outer surface. Such an electroconductive film is formed, for example, by applying an electroconductor solution and heating the coating, or by vacuum deposition or sputtering.
In order to prevent the reflection of external light, the glassy surface of the panel is etched with hydrofluoric acid to form minute irregularities, thereby imparting a reflection-inhibiting function. In recent years, an alcohol solution containing Si(OR).sub.4 is spray-coated on the outer surface of the panel to form numerous fine projections.
Japanese Laid-Open Publication No. 61-118932 discloses a cathode ray tube having an antistatic and non-glare coating in which an alcohol solution of Si(OR).sub.4 is spray-coated on the outer surface of a panel and heated at 150.degree. C. or less, to form a non-glare surface of SiO.sub.2 film having silanol groups. Since the heating temperature is relatively low, some silanol groups (.tbd.Si--OH) remain in the siloxane structure (.tbd.Si--O--Si.tbd.), and the hygroscopic nature of the --OH group endows the film with antistatic properties.
U.S. Pat. No. 4,945,282 discloses a process for producing image display panels which comprises the step of: applying a suspension of fine particles of at least one of an electroconductive metal oxide (SnO.sub.2, In.sub.2 O.sub.3, Sb.sub.2 O.sub.3) and hygroscopic metal salts in an alcoholic solution of alkoxysilane on the front surface of the panel, followed by heat treatment of the resulting coating to form an antistatic film. This process may further comprise the step of forming a thin non-glare film of SiO.sub.2 on the antistatic film.
According to the method of spraying an alcohol solution of Si(OR).sub.4 and heating to form a non-glare coating of SiO.sub.2 having minute projections or depressions, sprayed liquid particles are not uniformly deposited, that is, they are more thickly deposited toward the periphery of the object panel surface.
For that reason and others (such as heating conditions), it is difficult to create a uniform degree of unevenness throughout the panel's surface. Such inconsistent unevenness of the surface coating results in an irregular non-glare effect to the panel, which in turn will cause lower degrees of resolution.